The present invention relates to a passing cell monitoring device operated with an ATM (Asynchronous Transfer Mode) Switching Unit in a B-ISDN (broadband ISDN).
Unlike a conventional switching unit, an ATM switching unit provides various types of services for subscribers. Since a subscriber's charge and the management of a switching unit's band depend on the types of services the switching unit provides, a supplier and a subscriber usually negotiate before determining the types of services to be provided.
According to the agreement between them, the switching unit provides the subscriber with an information switching service in a predetermined band.
If the subscriber transmits for some reasons the information of the band beyond the predetermined speed to the switching unit, the switching unit will be subject to abnormal conditions such as information confusion, etc. due to an illegal usage of the band resources of the switching unit. To prevent such abnormal situations, a regulating process referred to as a "police" is performed.
In the regulating process "police", a subscriber corresponder of the switching unit counts according to a virtual path identifier/virtual channel identifier (VPI/VCI), the number of cells passing within a predetermined period, compares the result with a predetermined threshold, and controls according to the result whether or not the cell being checked can be passed. This process is controlled according to the hardware logic.
The observation data to be used in performing the "police" function include average band, maximum band, and burst retaining period data. Therefore, in the above device in which the number of cells passing within a predetermined time period is counted and the result is compared with a predetermined threshold, each parameter is calculated based on the number of cells passing within the predetermined period. At some unit time, the counting operation may not be able to keep up with the fluctuation of the number of passing cells. Therefore, it is very difficult to obtain a reliable police function in the prior art technology. That is, the number of passing cells always fluctuates. Sometimes, a lot of cells pass and then none pass. The conventional device cannot handle such a condition, and can not perform a reliable police function.